Certain types of structural assemblies require additional features for strength reinforcement of the structural assembly. For example, in an aircraft cargo hold, corner fittings may be installed at the beam joints of intersecting floor beams to reinforce the floor beams against vertical uploads imposed by cargo on the floor of the cargo hold. Such corner fittings are conventionally formed of metallic material and may be fastened to the floor beams to transfer vertical tension loads from cargo tie-downs into the vertical webs of the floor beams. Unfortunately, such metallic corner fittings are relatively heavy compared to those made from composite materials. In addition, metallic corner fittings provide minimal energy-absorbing capability in a vertical direction as may be desired in a high-strain-rate compression-loading event such as an aircraft impact event.
Structures formed of composite material are advantageous due to their high strength-to-weight ratio, favorable corrosion resistance, and high specific energy-absorbing capability during compression-loading events. A composite corner fitting may be formed by laying up composite plies comprised of reinforcing fibers embedded in a polymer matrix. Composite structures are typically designed to transmit loads along the length of the reinforcing fibers. Loads from one fiber may be transferred to another fiber in the same layer or to fibers in an adjacent layer by passing through the matrix material. However, the matrix is typically weaker than the fibers such that when a sufficiently-high load is placed on the composite structure in an out-of-plane direction or in a direction non-parallel to the fibers, the matrix may fail.
In conventional composite structures, the composite plies are typically aligned with and define the outer geometry of the structure. Unfortunately, a composite structure may be subjected to loads that are oriented non-parallel to the fibers and/or in an out-of-plane direction relative to the plane of the composite plies. Such non-parallel and out-of-plane loads may result in interlaminar tension effects that may exceed the load-carrying capability of the composite structure. In order to avoid overloading the composite structure, additional composite plies may be required which may increase the weight and complexity of the composite structure.
As can be seen, there exists a need in the art for a composite corner fitting capable of efficiently transferring tension load into a web of a beam while avoiding interlaminar tension effects in the corner fitting.